The present inventive concept herein relates to an image extraction, and more particularly, to an optical phase extraction system forming an interferometer using an optical fiber and a three-dimensional image extraction method thereof.
To measure very little displacement or vibration in real time in a wide area with respect to a measuring object, a laser interference method having a high spatial decomposition rate is often used.
A three-dimensional shape information measurement method using a laser interference method may be divided into an electronic speckle pattern interferomety (ESPI) and a searography according to a measuring object and a measuring environment. Also, the laser interferometer is divided into an optical fiber type and a bulk type according to the type of optical device being used.
The bulk type interferometer has disadvantages of large volume and great optical loss while in the optical fiber type interferometer, an optical arrangement can be easily performed and optical elements applied thereto are small and light. Thus, the optical fiber type interferometer has advantages that its portability is good and it can be easily made.
An EPI system having an optical fiber type interferometer is disclosed in a U.S. Pat. No. 6,043,870. To extract three-dimensional shape information of measuring object, a process of operating CCD images obtained at the state that the measuring object is phase-shifted is needed. Thus, the ESPI system adopts a phase modulator. A technique improving contrast of images using a pulse image supplementary ESPI technique without the use of phase modulator is disclosed in U.S. Pat. No. 6,362,873.
Since most of phase modulators used in a phase shift of interferometer to acquire an image have a nonlinear operation characteristic, an arrangement of optical system becomes in disorder whenever it is measured. Thus, a phase compensation measure is needed to remove or minimize generated phase measuring errors.
In case of the optical fiber type interferometer, the change of optical output of interferometer is great because it is sensitive to an environment, that is, disturbance including, for example, temperature, humidity, vibration or strain. Thus, that is becoming one of the obstacles to commercialization of system because of the difficult of field application.